The present invention relates to a hydraulic pressure compensating method and device for a pressure-equalizing apparatus for pressure pins of a pressing machine.
A pressing machine is a machine for forming a work piece such as a metal plate, which is carried in, between a vertically movable upper die and a lower die placed to face the upper die. An outline of a pressing machine equipped with a conventional pressure-equalizing apparatus for pressure pins (for example, Japanese Patent No. 2705393) will be explained with reference to FIGS. 6 and 7. FIG. 7 is an enlarged view of a pressure-equalizing apparatus illustrated in FIG. 6.
An upper die 1 is attached on an underside surface of a slide 2 movable up and down by means of a slide driving mechanism (not illustrated). A press carrier 5 is movably placed on a bed 50 of the pressing machine, and a bolster 4 is placed on a top portion of the press carrier 5. The bed 50 is equipped with a die cushion device 9, a cushion cylinder 9b fixed to a cushion rod 9j inside the die cushion device 9 is movable up and down. A cushion pad 10 is placed on the cushion cylinder 9b so as to be in contact therewith and separate therefrom, and a pressure-equalizing plate 26 is attached on the cushion pad 10. A plurality of pressure-equalizing cylinders 8 are attached on the top surface of the pressure-equalizing plate 26, and a pressure-equalizing piston 8b is slidably inserted in each of the pressure-equalizing cylinders 8. A lower end portion of a pressure pin 7 abuts to the pressure-equalizing piston 8b, and an upper end surface of each pressure pin 7 supports a lower die 3.
An oil chamber 8d of each of the pressure-equalizing cylinders 8 communicates with a pressure-equalizing circuit 42 formed inside the pressure-equalizing plate 26, and the pressure-equalizing circuit 42 is connected with a hydraulic pump 25 via a pipe line 15. The applied pressure, which is applied when the descending upper die 1 forms a work piece 18, is transmitted to the oil chambers 8d of a plurality of the pressure-equalizing cylinders 8 via a plurality of the pressure pins 7 and the pistons 8b, and the applied pressure is equalized by a plurality of the pressure-equalizing cylinders 8 communicated with one another.
An air chamber 52 defined by a cushion piston 9a and the cushion cylinder 9b is supplied with air of predetermined air pressure from an air source 9f via a regulator 9g and an air tank 9h. The cushion rod 9j penetrating in an axial direction is placed at a center portion of the cushion cylinder 9b, and an upper end of the cushion rod 9j is fixed to the cushion cylinder 9b. 
In the pressing machine equipped with the pressure-equalizing apparatus for the pressure pins having the configuration as above, a hydraulic control of the oil chamber 8d of each pressure-equalizing cylinder 8 to equalize the applied pressure is carried out in accordance with a method shown in FIG. 8.
The oil chamber 8d of each pressure-equalizing cylinder 8 communicates with one another via the pressure-equalizing circuit 42 of the pressure-equalizing plate 26. An electromagnetic valve 20 is placed at an inlet side of a hydraulic port at one end of the pressure-equalizing circuit 42, and an electromagnetic valve 21 is placed at an outlet side of the hydraulic port at the other end. The oil of an oil tank 29 is fed to the pressure-equalizing circuit 42 via the electromagnetic valve 20 at the inlet side by means of the hydraulic pump 25, and the pressure oil from the electromagnetic valve 21 at the outlet side is returned to the oil tank 29. The electromagnetic valve 20 at the inlet side and the electromagnetic valve 21 at the outlet side have two positions: an electromagnetic valve open position 27 and an electromagnetic valve closed position 28. The electromagnetic valve operates in the electromagnetic valve closed position 28 when an off signal is inputted, and it operates in the electromagnetic valve open position 27 when an on signal is inputted.
A hydraulic pressure signal detected by a hydraulic pressure detector 22 for detecting the hydraulic pressure at the hydraulic port at the other end of the pressure-equalizing plate 26, and a positional signal from a position detector 24 for detecting the position of the slide 2 are inputted into a controller 23. On/off signals to the electromagnetic valve 20 at the inlet side and the electromagnetic valve 21 at the outlet side are outputted from the controller 23 respectively.
When the slide 2 with the upper die 1 being attached thereto descends to form the work piece 18, the electromagnetic valve 20 at the inlet side and the electromagnetic valve 21 at the outlet side remain in the electromagnetic valve closed position 28. When the position detector 24 detects that the slide 2, which has completed forming, ascends and reaches approximately the upper dead center, the on/off signals are outputted to the electromagnetic valve 20 at the inlet side and the electromagnetic valve 21 at the outlet side. In this situation, when the on signal is outputted to the electromagnetic valve 20 at the inlet side, the OFF signal is outputted to the electromagnetic valve 21 at the outlet side, and the ON/OFF signals are alternately and repeatedly outputted in this manner so that the control is carried out to make the hydraulic value detected by the hydraulic pressure detector 22 approach a predetermined hydraulic value.
When the hydraulic value detected by the hydraulic pressure detector 22 is sufficiently close to the predetermined hydraulic value, both the electromagnetic valve 20 at the inlet side and the electromagnetic valve 21 at the outlet side are in the closed position 28, and the hydraulic pressures of the oil chambers 8d of all the pressure-equalizing cylinders 8 are maintained at the predetermined hydraulic value.
In the above art, however, the following disadvantage arises.
The electromagnetic valve 20 at the inlet side and the electromagnetic valve 21 at the outlet side are mounted near the pressure-equalizing plate 26 to make it easy to control the hydraulic pressures of the pressure-equalizing cylinders 8 at predetermined hydraulic pressure. Since the pressure-equalizing plate 26 is placed on a cushion pad 10, which is always subjected to vigorous vibrations and impacts, the electromagnetic valve 20 at the inlet side and the electromagnetic valve 21 at the outlet side are always subjected to the vigorous vibrations and impacts. Iron powders and oil splashes come into and scatter at the top portions of the pressure-equalizing cylinders 8 placed under the bolster 4 from holes in the bolster 4 in which the pressure pins 7 ascend and descend. Hence, the electromagnetic valve 20 at the inlet side and the electromagnetic valve 21 at the outlet side are always exposed to an atmosphere with iron powders and oil splashes. As a result, oil enters the electromagnetic valve 20 at the inlet side and the electromagnetic valve 21 at the outlet side to frequently produce trouble, thus causing the disadvantage of reducing availability of the pressing machine.
The present invention is made in view of the aforementioned disadvantage, and its object is to provide a pressing machine with fewer breakdowns in a hydraulic pressure compensating device for a pressure equalizing apparatus.
In order to attain the above object, a hydraulic pressure compensating method for a pressure-equalizing apparatus for pressure pins according to the present invention is a hydraulic pressure compensating method for a pressure-equalizing apparatus for pressure pins, for compensating a hydraulic pressure value of a pressure-equalizing circuit by connecting oil feeding means to a pressure-equalizing circuit, which is provided between a lower die and a die cushion device of a pressing machine, and which is communicated with oil chambers of a plurality of pressure-equalizing cylinders for equalizing applied pressure to a work piece during a forming operation to thereby equalize hydraulic pressure, and including the steps of
connecting the pressure-equalizing circuit and the oil feeding means according to hydraulic pressure of the pressure-equalizing circuit and predetermined preloading pressure at an outlet port of the oil feeding means to thereby set the hydraulic pressure of the pressure-equalizing circuit at the preloading pressure, when the hydraulic pressure of the pressure-equalizing circuit decreases after the completion of the forming operation from peak pressure at the time of completion of the forming, and becomes smaller than a predetermined value, and
after setting the same at the preloading pressure, disconnecting the oil feeding means and the pressure-equalizing circuit, and continuing the disconnection until the hydraulic pressure of the pressure-equalizing circuit in an next forming operation decreases from the peak pressure and becomes smaller than the predetermined value once again.
According to the above configuration, at the time of completion of the forming of the work piece, the hydraulic pressure inside the pressure-equalizing cylinders has a large peak value, and decreases as it is pulsing. When the hydraulic pressure decreases and becomes smaller than a predetermined value, the oil feeding means is connected to the pressure-equalizing circuit according to the hydraulic pressure of the pressure-equalizing circuit and the preloading pressure. Thereupon, the preloading pressure is exerted on the pressure-equalizing circuit from the oil feeding means. Since a plurality of pressure-equalizing cylinders is connected to the pressure-equalizing circuit, the hydraulic pressures of all the pressure-equalizing cylinders become the preloading pressures. After the hydraulic pressures of all the pressure-equalizing cylinder are set at the preloading pressure, the communication with the oil feeding means is shut off according to the hydraulic pressure of the pressure-equalizing circuit and the preloading pressure. The shutoff of the communication is continued until the hydraulic pressure of the pressure-equalizing circuit at the time of the next forming operation decreases and becomes smaller than the predetermined value once again. As described above, the hydraulic pressures of all the pressure-equalizing cylinders are reset at the preloading pressure for each cycle of the forming operation with the hydraulic pressure of the pressure-equalizing cylinders as a signal. As described above, since the method is for mechanically compensating the hydraulic pressure of the pressure-equalizing cylinders with the hydraulic pressure of the pressure-equalizing cylinder as an input signal, the mechanical type of on-off valve, the switching cylinder and the on-off valve driving mechanism do not break down, even if oil enters them when they are subjected to vigorous vibrations and impacts and operated in an atmosphere with iron powders and oil splashes. As a result, failure of the pressure compensating device is decreased, thus making it possible to obtain the pressing machine with higher availability.
A hydraulic pressure compensating device for a pressure-equalizing apparatus for pressure pins according to the present invention is a hydraulic pressure compensating device for a pressure-equalizing apparatus for pressure pins including a plurality of pressure pins for supporting a lower die of a pressing machine, a plurality of pressure-equalizing cylinders, which support the respective pressure pins and are communicated with one another via a pressure-equalizing circuit for equalizing hydraulic pressure, and oil feeding means for feeding oil to the pressure-equalizing circuit, and has the configuration including:
a mechanical on-off valve for opening and closing communication between an outlet port of the oil feeding means having predetermined preloading pressure and the pressure-equalizing cylinders;
a switching cylinder with a bottom chamber being connected to the outlet port of the oil feeding means and a head chamber having a smaller pressure receiving area than that of the bottom chamber being connected to the pressure-equalizing circuit; and
an on-off valve driving mechanism for operating the on-off valve to an open position and thereafter returning the same to a closed position, in an extension process in which the switching cylinder is extended when the hydraulic pressure of the pressure-equalizing circuit decreases from peak pressure at the completion of a forming operation and becomes smaller than a predetermined value and the product of the preloading pressure and a pressure receiving area of the bottom chamber becomes larger than the product of hydraulic pressure of the pressure-equalizing cylinder and the pressure receiving area of the head chamber, and for always holding the on-off valve in a closed position in a process in which the switching cylinder is retreated.
According to the above configuration, when the upper die descends from the top dead center and the forming of the work piece is completed, and when the upper die ascends after the completion of the forming, the switching cylinder is extended and contracted with the hydraulic pressure varying inside the pressure-equalizing cylinders as an signal. The on-off valve driving mechanism opens and closes the on-off valve and controls the hydraulic pressure of the pressure-equalizing cylinders based on the extending and contracting amount of the switching cylinder. As described above, with the totally mechanical type of pressure compensating device for the pressure-equalizing apparatus for pressure pins, even if oil enters the mechanical on-off valve, the switching cylinder, and the on-off valve driving mechanism when they are subjected to vigorous vibrations and impacts and operated in an atmosphere with iron powders and the oil splashes, they do not break down. Consequently, the breakdown of the pressure-compensating device is decreased, thus making it possible to obtain the pressing machine with higher availability.